Imaging moir\'e flat bands in 3D reconstructed WSe2/WS2 superlattices

TL;DR

This study combines experimental scanning tunneling spectroscopy with ab initio simulations to reveal the 3D structural reconstruction and resulting narrow moiré flat bands in WSe2/WS2 heterostructures, advancing understanding of correlated quantum phenomena.

Contribution

It provides the first detailed experimental and theoretical analysis of 3D reconstructed moiré superlattices in TMD heterostructures, highlighting the importance of strain and buckling effects.

Findings

Identification of strong 3D buckling and strain redistribution in the heterostructures

Observation of highly localized moiré flat bands at the valence band edge

Quantitative agreement between experiments and ab initio simulations

Abstract

Moir\'e superlattices in transition metal dichalcogenide (TMD) heterostructures can host novel correlated quantum phenomena due to the interplay of narrow moir\'e flat bands and strong, long-range Coulomb interactions1-5. However, microscopic knowledge of the atomically-reconstructed moir\'e superlattice and resulting flat bands is still lacking, which is critical for fundamental understanding and control of the correlated moir\'e phenomena. Here we quantitatively study the moir\'e flat bands in three-dimensional (3D) reconstructed WSe2/WS2 moir\'e superlattices by comparing scanning tunneling spectroscopy (STS) of high quality exfoliated TMD heterostructure devices with ab initio simulations of TMD moir\'e superlattices. A strong 3D buckling reconstruction accompanied by large in-plane strain redistribution is identified in our WSe2/WS2 moir\'e heterostructures. STS imaging demonstrates that this results in a remarkably narrow and highly localized K-point moir\'e flat band at the valence band edge of the heterostructure. A series of moir\'e flat bands are observed at different energies that exhibit varying degrees of localization. Our observations contradict previous simplified theoretical models but agree quantitatively with ab initio simulations that fully capture the 3D structural reconstruction. Here the strain redistribution and 3D buckling dominate the effective moir\'e potential and result in moir\'e flat bands at the Brillouin zone K points.